Earth scale environment problems such as global warming and destruction of the ozone layer are largely highlighted. In particular, the CO2 reduction that is said to largely affect on the warming of the earth as a whole is gathering attention on how to decide the regulation value in each country.
As to the CO2 reduction, the reduction of the energy loss due to the friction loss of machines and devices, in particular, the reduction of the fuel cost of automobiles is a large problem. Accordingly, the roles of sliding materials and lubricants are very important in this connection.
A role of the sliding material is to be excellent in the wear resistance and develop excellent wear resistance to sections of which friction and wear environment are severe among the sliding sections of an engine. Recently, various kinds of hard thin film materials are being forwarded in applications. The friction coefficients of general DLC materials are lower in air and in the absence of lubricating oil than that of wear resistant hard coating materials such as TiN and CrN; accordingly, these are expected as low friction sliding materials.
Furthermore, as an energy saving measure in the lubricating oil, for instance, as a fuel efficiency measure of an engine, 1) reduction, caused by lowering the viscosity, of the viscous resistance in a hydrodynamic lubrication region and the agitation resistance in an engine and 2) reduction, owing to blending of an optimum friction modifier and various kinds of additives, of the friction loss under mixed lubrication and boundary lubrication region are proposed. Many researches have been conducted mainly of organic Mo compounds such as MoDTC and MoDTP as the friction modifier. In a sliding surface made of an existing steel material, a lubricating oil composition in which an organic Mo compound that exhibits the excellent low friction coefficient at an early stage of use is advantageously applied.
On the other hand, a general DLC material excellent in the low friction characteristics in air is reported to be, in the presence of the lubricating oil, low in the friction reduction effect (for instance, non-patent literature 1). Furthermore, it has been found that even when a lubricating oil composition containing an organic molybdenum compound is applied to the sliding material the friction reduction effect cannot be sufficiently exerted (for instance, non-patent literature 2).    Non-patent literature 1: Kano et al., Proceedings of Japanese Tribology Society, p. 11 to 12, May, 1999 (Tokyo)    Non-patent literature 2: Kano et al., Proceeding of World Tribology Congress September, 2001, p. 342, (Vienna)
Then, as to the fuel efficient technology of a manual transmission of an automobile, there is a proposal in which the agitation of lubricating oil by a power transfer is avoided or made very small to inhibit the power transmission efficiency from deteriorating owing to the agitation resistance (for instance, patent literature 1).    Patent literature 1: JP-A-10-166877
On the other hand, as to the lubricating oil that is used in such a transmission, a lubricating oil composition in which, to lubrication base oil a boron-containing ash-less dispersant, an alkaline-earth metal base detergent and a sulfur base additive are blended is proposed (patent literature 2). Furthermore, gear oil in which, to base oil that is low in a sulfur content and has predetermined viscosity, primary zinc dithiophosphate, an alkaline earth metal detergent, alkenyl succinic imide having a polybutenyl group having a predetermined molecular weight, a derivative thereof, phosphoric ester amine salt, and a sulfur compound are contained is proposed (patent literature 3).    Patent literature 2: JP-A-2003-82377    Patent literature 3: JP-A-11-181463
Furthermore, as to the fuel efficient technology of the final reduction gear unit of an automobile, with an intention of improving the transmission efficiency at a differential gear, a lubricating oil composition for use in the final reduction gear unit, which contains a phosphorus base extreme pressure agent selected from a specific range, organic acids having a specific structure and a sulfur base extreme pressure agent selected from a specific range in a lubrication base oil, is proposed (patent literature 4).    Patent literature 4: JP-A-6-200274
Still furthermore, in order to reduce the sliding friction loss between a roller end surface and an inner wheel large guard, a conical roller bearing where a cone center of an outer diameter surface of a conical roller is displaced from a center axis of the inner wheel and the application of such conical roller bearing to an automobile differential are proposed (patent literature 5).    Patent literature 5: JP-A-2000-192951